System and method for systolic interval analysis

ABSTRACT

A system and method provide for systolic interval analysis. In an example, an implantable device measures a cardiac impedance signal. A transformation of the cardiac impedance interval is generated. The device also measures a heart sound signal. A time interval between a point on the transformed signal of the cardiac impedance signal and a point on the heart sound signal is calculated.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to Patangay, U.S. patent application Ser. No.11/553,179, entitled “System and Method for Systolic Interval Analysis,”filed on Oct. 26, 2003, which is hereby incorporated by reference hereinin its entirety.

TECHNICAL FIELD

The present disclosure relates to an implantable medical device system,and in an embodiment, but not by way of limitation, an implantablemedical device system and method that analyzes systolic intervals.

BACKGROUND

The heart is at the center of the circulatory system. It includes fourchambers—two atria and two ventricles. The right atrium receivesdeoxygenated blood from the body, pumps it into the right ventricle, andthe right ventricle pumps the blood to the lungs to be re-oxygenated.The re-oxygenated blood returns to the left atrium, it is pumped intothe left ventricle, and then the blood is pumped by the left ventriclethroughout the body to meet the hemodynamic needs of the body.

The heart includes a sino-atrial node that generates a depolarizationwave that propagates through the heart. The depolarization wave can besensed in the heart or at the surface of the body. The depolarizationwave of a full cardiac cycle includes a P wave, a QRS complex, and a Twave. The P wave represents the atrial depolarization before the atrialcontraction, and the QRS complex represents the ventriculardepolarization before the ventricular contraction. The T wave representsthe ventricular repolarization as the ventricles recover from thedepolarization.

Heart sounds are associated with mechanical vibrations from activity ofa patient's heart and the flow of blood through the heart. Heart soundsrecur with each cardiac cycle and are separated and classified accordingto the activity associated with the vibration. The first heart sound(S1) is associated with the vibrational sound made by the heart duringtensing of the mitral valve. The second heart sound (S2) marks thebeginning of diastole. The third heart sound (S3) and fourth heart sound(S4) are related to filling pressures of the left ventricle duringdiastole. Heart sounds are useful indications of proper or improperfunctioning of a patient's heart.

Implantable medical devices (IMDs) are devices designed to be implantedinto a patient. Some examples of these devices include cardiac functionmanagement (CFM) devices such as implantable pacemakers, implantablecardioverter defibrillators (ICDs), cardiac resynchronization devices,and devices that include a combination of such capabilities. The devicesare typically used to treat patients using electrical therapy or to aida physician or caregiver in patient diagnosis through internalmonitoring of a patient's condition. The devices may include electrodesin communication with sense amplifiers to monitor electrical heartactivity within a patient, and often include sensors to monitor otherinternal patient parameters. Other examples of implantable medicaldevices include implantable diagnostic devices, implantable insulinpumps, devices implanted to administer drugs to a patient, orimplantable devices with neural stimulation capability.

Overview

An implantable medical device can be used to detect cardiac impedancesignals and heart sound signals. The device can calculate a timeinterval between a point on the heart sound signal and a point on thecardiac impedance signal. The time interval can be compared toindependently specifiable thresholds, such as to trigger an alert orresponsive therapy, or to display one or more trends. The time intervalinformation can also be combined with detection of one or more othercongestive heart failure (CHF) symptoms to generate a CHF statusindicator or to trigger an alarm or responsive therapy or to display oneor more trends. The alert can notify a patient or a caregiver, such asvia remote monitoring.

In Example 1, a system includes an implantable medical device. Theimplantable medical device includes a timing circuit, a cardiacimpedance sensing circuit that is coupled to the timing circuit and thatis configured to detect a cardiac impedance signal, an acoustic sensorthat is coupled to the timing circuit and that is configured to sense anacoustic signal, and a heart sound detector circuit that is coupled tothe timing circuit and that is configured to detect a heart sound signalin the acoustic signal. The timing circuit is configured to calculate atime interval between a point on the heart sound signal and a point onthe cardiac impedance signal.

In Example 2, the system of Example 1 optionally includes a telemetrycircuit that is coupled to the timing circuit and that is configured totransmit one or more of heart sound data and cardiac impedance data toone or more of an external device and an external database.

In Example 3, the systems of Examples 1-2 optionally include a transformcircuit that is coupled to the timing circuit and that is configured tocalculate a transformed signal of the cardiac impedance signal. InExample 3, the timing circuit is optionally configured to calculate atime interval between a point on the heart sound signal and a point onthe transformed signal.

In Example 4, the timing circuits of Examples 1-3 are optionallyconfigured to calculate a time interval between a point on the heartsound signal and a point on the transformed signal that calculates aleft ventricular ejection time. In Example 4, in the calculation of theleft ventricular ejection time the timing circuit optionally uses apoint on the heart sound signal indicative of an S1 heart sound, and apoint on the transformed signal indicative of an aortic valve closurewithin a cardiac cycle.

In Example 5, the timing circuits of Examples 1-4 are optionallyconfigured to calculate a time interval between a point on the heartsound signal and a point on the transformed signal that calculates anestimate of pre-ejection time. In Example 5, in the calculation of theestimate of the pre-ejection time, the timing circuit optionally uses apoint on the heart sound signal indicative of an S4 heart sound, and apoint on the transformed signal indicative of an aortic valve openingwithin a cardiac cycle.

In Example 6, the timing circuits of Examples 1-5 are optionallyconfigured to calculate the time interval between a point on the heartsound signal indicative of an S4 heart sound, and a point on thetransformed signal indicative of a maximum systolic blood flow within acardiac cycle.

In Example 7, the timing circuits of Examples 1-6 are optionallyconfigured to calculate the time interval between a point on the heartsound signal indicative of an S2 heart sound; and a point on thetransformed signal indicative of one of a maximum systolic blood flowwithin a cardiac cycle, an aortic valve opening within a cardiac cycle,a pulmonary valve closure within a cardiac cycle, an aortic valveclosure within a cardiac cycle, or a mitral valve opening within acardiac cycle.

In Example 8, the timing circuits of Examples 1-7 are optionallyconfigured to calculate the time interval between a point on the heartsound signal indicative of an S1 heart sound; and a point on thetransformed signal indicative of one of an aortic valve opening within acardiac cycle, a pulmonary valve closure within a cardiac cycle, or amitral valve opening within a cardiac cycle.

In Example 9, the timing circuits of Examples 1-8 are optionallyconfigured to calculate the time interval between a point on the heartsound signal indicative of an S3 heart sound; and a point on thetransformed signal indicative of one of an aortic valve closure within acardiac cycle, a pulmonary valve closure within a cardiac cycle, or amitral valve opening within a cardiac cycle.

In Example 10, the timing circuits of Examples 1-9 are optionallyconfigured to calculate the time interval over multiple cardiac cycles,and to identify or characterize a decompensation as a function of one ormore changes in the time interval over the multiple cardiac cycles.

In Example 11, the systems of Examples 1-10 optionally include anexternal device. The implantable medical device optionally includes acardiac sensing circuit that is coupled to the timing circuit and thatis configured to detect a cardiac signal; an ensemble averaging circuitthat is coupled to the timing circuit and that is configured to generatean ensemble average for one or more of the cardiac signal, the cardiacimpedance signal, the heart sound signal, and the transformed signal;and a telemetry circuit. The cardiac signal can be a cardiac electricsignal (EGM). The external device optionally includes a telemetrycircuit; a memory circuit configured to store one or more of theensemble averaged cardiac signal, the ensemble averaged cardiacimpedance signal, the ensemble averaged heart sound signal, and theensemble averaged transformed signal; and a timing circuit configured tocalculate a second time interval between one or more of (1) a point onthe ensemble averaged cardiac signal and a point on the ensembleaveraged heart sound signal, (2) a first point on the ensemble averagedheart sound signal and a second point on the ensemble averaged heartsound signal, (3) a point on the ensemble averaged impedance signal anda point on the ensemble averaged heart sound signal, and (4) a point onthe ensemble averaged heart sound signal and a point on the ensembleaveraged transformed signal.

In Example 12, in the system of Example 11, the point of the ensembleaveraged cardiac signal optionally includes a portion of an R wave, andthe point of the ensemble averaged heart sound signal is optionallyindicative of one of an S1, S2, S3, or S4 heart sound.

In Example 13, the external device memory of Examples 11-12 optionallyinclude one or more of cardiac signal data, cardiac impedance data,heart sound data, and transformed signal data from a population ofindividuals. The external device is optionally configured to use thecardiac signal, cardiac impedance, heart sound, and transformed signalpopulation data in connection with an analysis of an individual'scardiac signal, cardiac impedance, heart sound, and transformed signaldata.

In Example 14, the external devices of Examples 11-13 optionally includeor are optionally coupled to one or more external sensors. One or morepatient thresholds are optionally set as a function of data receivedfrom the one or more external sensors.

In Example 15, the external devices of Examples 11-14 optionally includeor are optionally coupled to one or more of an external sensor and adatabase. The external device further optionally includes a circuitconfigured to compare one or more of the cardiac signal, the cardiacimpedance signal, the heart sound signal, the transformed signal, datafrom the external sensor, and data from the database.

In Example 16, the external sensors of Examples 11-15 optionally includeone or more of a body weight sensor and a blood pressure sensor. Thedatabase optionally includes one or more of a medication history, adisease history, a hospitalization history, and one or more populationstatistics.

In Example 17, a process includes measuring a cardiac impedance signalwith an implantable medical device, measuring a heart sound signal withthe implantable medical device, and calculating a time interval betweena point on the cardiac impedance signal a point on the heart soundsignal.

In Example 18, the process of Example 17 optionally includestransforming the cardiac impedance signal into a transformed signal, andcalculating a time interval between a point on the transformed signaland a point on the heart sound signal. The transforming may include oneor more of a differentiation, a filtering, a derivation, and anintegration.

In Example 19, in the processes of Examples 17-18, the calculation ofthe time interval between a point on the transformed signal of thecardiac impedance signal and a point on the heart sound signaloptionally calculates a left ventricular ejection time. The calculationof the left ventricular ejection time optionally uses a point on theheart sound signal indicative of an S1 heart sound, and a point on thetransformed signal indicative of an aortic valve closure within acardiac cycle.

In Example 20, in the processes of Examples 17-19, the calculation of atime interval between a point on the transformed signal of the cardiacimpedance signal and a point on the heart sound signal optionallyestimates a pre-ejection time. The estimation of the pre-ejection timeoptionally uses a point on the heart sound signal indicative of an S4heart sound, and a point on the transformed signal indicative of anaortic valve opening within a cardiac cycle.

In Example 21, in the processes of Examples 17-20, the calculation ofthe time interval optionally uses a point on the heart sound signalindicative of an S4 heart sound, and a point on the transformed signalindicative of a maximum systolic blood flow within a cardiac cycle.

In Example 22, in the processes of Examples 17-21, the calculation ofthe time interval optionally uses a point on the heart sound signalindicative of an S2 heart sound; and a point on the transformed signalindicative of a maximum systolic blood flow within a cardiac cycle, anaortic valve opening within a cardiac cycle, a pulmonary valve closurewithin a cardiac cycle, an aortic valve closure within a cardiac cycle,or a mitral valve closure within a cardiac cycle.

In Example 23, in the processes of Examples 17-22, the calculation ofthe time interval optionally uses a point on the heart sound signalindicative of an S1 heart sound; and a point on the transformed signalindicative of one of an aortic valve opening within a cardiac cycle, apulmonary valve closure within a cardiac cycle, or a mitral valveopening within a cardiac cycle.

In Example 24, in the processes of Examples 17-23, the calculation ofthe time interval optionally uses a point on the heart sound signalindicative of an S3 heart sound; and a point on the transformed signalindicative of one of an aortic valve closure within a cardiac cycle, apulmonary valve closure within a cardiac cycle, or a mitral valveopening within a cardiac cycle.

In Example 25, the processes of Examples 17-24 optionally includecalculating the time interval over multiple cardiac cycles, andidentifying or characterizing a decompensation as a function of a changein the time interval over the multiple cardiac cycles.

This overview is intended to provide an overview of the subject matterof the present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the subjectmatter of the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an implanted medical device incommunication with an adjunct device.

FIG. 2 illustrates an example of an implantable medical device.

FIG. 3A illustrates an example of a cardiac signal.

FIG. 3B illustrates an example of a cardiac impedance signal.

FIG. 3C illustrates an example of a first derivative of a cardiacimpedance signal.

FIG. 3D illustrates an example of a heart sound signal.

FIG. 4 illustrates an example of a process to calculate systolic timeintervals.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the disclosure may bepracticed. These embodiments, which are also referred to as examples,are discussed in sufficient detail to enable those skilled in the art topractice the disclosure, and it is to be understood that the embodimentsmay be combined, or that other embodiments may be utilized and thatstructural, logical and electrical changes may be made without departingfrom the scope of the present disclosure. The following detaileddescription provides examples, and the scope of the present disclosureis defined by the appended claims and their equivalents.

It should be noted that references to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.

FIG. 1 is a diagram illustrating an example of a medical device system100 that can be used in connection with transmitting data from animplanted device 110 to an adjunct device 160. In an example, theadjunct device 160 is an external device. FIG. 1 illustrates a body 102with a heart 105. System 100 typically includes the implantable medicaldevice 110, a lead system 108, the adjunct device or system 160, and awireless telemetry link 170. Data can be transferred from the device 110to the adjunct system 160 via the telemetry link 170. As illustrated inFIG. 2, the adjunct device 160 may include a processor 161, a telemetrycircuit 162, a memory circuit 164, a timing circuit 166, an externalsensor 168, and a database 169. The telemetered data may be stored in amemory 164, and may then be used for analysis and interpretation eitherimmediately or at a later time.

FIG. 2 illustrates an example of the implantable medical device 110. Themedical device 110 includes a controller circuit 205. A cardiacimpedance sensing circuit 210 is connected to the controller circuit205. In an example, the cardiac impedance sensing circuit 210 isconfigured to detect a cardiac impedance signal from a heart. Thecontroller circuit 205 is further connected to a transform circuit 215.The transform circuit 215 may be configured to generate, for example,one or more of a derivative waveform, a filtered waveform, or anintegrated waveform of a cardiac impedance signal sensed by the cardiacimpedance sensing circuit 210. This transformation may be implementedwith, for example, a differentiator, a filter (e.g., linear, high pass,low pass, band pass), a derivative circuit, or an integrator circuit. Anacoustic sensor 220 is connected to the controller circuit 205. Theacoustic sensor 220 may be configured to sense an acoustic signal, andin particular, an acoustic signal generated by a contracting heart. Theacoustic sensor 220 may be one or more of several different types ofsensors including a microphone, an accelerometer, and a transducer. Aheart sound detector circuit 225 is connected to the controller circuit205. The heart sound detector circuit 225 is primarily configured todetect a heart sound signal in the acoustic signal from the acousticsensor 220. Also coupled to the controller circuit 205 is a timingcircuit 230. The timing circuit 230 is configured to calculate a timeinterval, such as between a point on a heart sound signal detected bythe heart sound detector circuit 225, and a point on the cardiacimpedance signal or a point on the transformed signal of the cardiacimpedance signal. A telemetry circuit 235 is connected to the controlcircuit 205. The telemetry circuit 235 can transmit data from theimplantable medical device 110 to an adjunct system, such as the adjunctsystem 160 in FIG. 1. Such transmitted data may include heart sound andother acoustic data, cardiac depolarization data, cardiac impedancedata, or transformed signals of the cardiac impedance data. Theimplantable device 110 may also include an electrical delivery circuit250, a drug dispensing circuit 255, or a neural stimulation circuit 260.

The implantable medical device 110 may further include a cardiac sensingcircuit 240. The cardiac sensing circuit 240 is coupled to thecontroller circuit 205, and may be configured to detect a cardiac signalgenerated by a heart. In an example, the implantable medical device 110may further include an ensemble averaging circuit 245 connected to thecontroller circuit 205. The ensemble averaging circuit 245 may beconfigured to generate an ensemble average for any electrical, acoustic,or other signals generated by the body in which the device 110 isimplanted, such as cardiac depolarization signals, cardiac impedancesignals, heart sound signals, or transformed signals of the cardiacimpedance signals. An ensemble average for a buffer of heart soundsignal data or other signal data may be generated, such as by a simplesummation of the acoustic sensor 220 outputs taken at a specified timerelative to a reference point such as a V-event marker. In an example,the ensemble average is of the amplitudes of the heart sound signal.

FIGS. 3A, 3B, 3C, and 3D illustrate examples of a cardiac signal 310, acardiac impedance signal 320, a first derivative 330 of the cardiacimpedance signal 320, and a heart sound signal 340 respectively. Thecardiac signal 310 includes a P wave 311, a Q wave 312, an R wave 313,an S wave 314, and a T wave 315. The cardiac impedance signal caninclude, within a particular cardiac cycle, an absolute maximum, anabsolute minimum, local minimums, local maximums, and other identifiablepoints and slopes (which may correspond to other points of other signalssuch as a cardiac signal or a first derivative of a cardiac impedancesignal). In this example, the first derivative 330 includes a first zerocrossing at 331, a cardiac cycle maximum at 332, a cardiac cycle minimumat 333, a local maximum and a local minimum at 334 and 335 respectively,and another local maximum at 336. The heart sound signal 340 includesthe S1 heart sound 341, the S2 heart sound 342, the S3 heart sound 343,and the S4 heart sound 344. FIGS. 3A-3D are illustrated such that apoint on one of the signal traces at a certain horizontal positionrepresents the same real time as a point on another one of the FIG. 3A,3B, 3C, or 3D graphs at the same horizontal position. However, while aparticular horizontal position on one graph represents the same time asthe same horizontal position on another graph, the position ofparticular features of each graph may change from cardiac cycle tocardiac cycle. For example, the horizontal position of the Q wave 312may change in relation to the maximum 332 of the first derivative 330.These changes represent time interval changes.

The cardiac impedance signal and the transformed signal of the cardiacimpedance signal may also relate to certain identifiable physiologicalevents. For example, in the first derivative of the cardiac impedancesignal illustrated in FIG. 3C, 331 is indicative of an aortic valveopening, 332 is indicative of a maximum systolic blood flow, 333 isindicative of an aortic valve closure, 334/335 is indicative of apulmonary valve closure, and 336 is indicative of a mitral valveopening.

The timing relationship of the signals in FIGS. 3A-3D permit acomparison of the time relationship of any point on one of the signals,e.g., the S4 heart sound signal 344 on the heart sound signal 340, andany point on another signal or transformed signal, e.g., the first zerocrossing 331 on the first derivative 330. For example, the timingcircuit 230, in conjunction with the heart sound detector circuit 225and the first derivative circuit 215, may be configured to calculate anytime interval between the first derivative 330 and the heart soundsignal 340. As another example, timing circuit 230 may calculate thetime interval between a point on the cardiac impedance signal 320 and apoint on the heart sound signal 340. As yet another example, the timingcircuit 230 may calculate the time interval between a point on the heartsound signal 340 and another other signal transformation of the cardiacimpedance signal 320.

For example, the timing circuit 230 may be configured to calculate aleft ventricular ejection time (LVET) time interval between a point onthe heart sound signal 340 and a point on the first derivative 330. Thecalculation of the LVET uses a point on the heart sound signalrepresenting the S1 heart sound 341, and a point on the first derivativerepresenting an absolute minimum 333 within a particular cardiac cycle.Similarly, an LVET may be calculated using a point on the heart soundsignal representing the S1 heart sound 341, and a point on a transformedcardiac impedance signal indicative of an aortic valve closure within acardiac cycle.

Similarly, the timing circuit 230 may be configured to calculate a timeinterval between a point on the heart sound signal 340 and a point onthe first derivative 330. The calculation of this time interval may usea point on the heart sound signal representing the S4 heart sound 344,and a point on the first derivative representing a first zero crossing331 within a cardiac cycle. Similarly, the calculation of this timeinterval may use a point on the heart sound signal representing the S4heart sound 344, and a point on a transformed cardiac impedance signalindicative of an aortic valve opening within a cardiac cycle.

Any time interval between any two points on one or more of the cardiacsignal 310, the cardiac impedance signal 320, the first derivativesignal 330, the heart sound signal 340, and a transformed cardiacimpedance signal may be calculated. For example, the timing circuit 230may be configured to calculate a time interval between a point on theheart sound signal 340 representing an S4 heart sound 344, and a pointon the first derivative representing an absolute maximum 332 within aparticular cardiac cycle. The timing circuit 230 may also be configuredto calculate a time interval between a point on the heart sound signal340 representing an S4 heart sound 344, and a point on a transformedcardiac impedance signal indicative of an aortic valve opening within acardiac cycle. As another example, the timing circuit 230 may beconfigured to calculate a time interval between a point on the heartsound signal 340 representing an S2 heart sound 342, and any one of thefollowing points on the first derivative signal 330—an absolute maximum332 within a cardiac cycle, a first zero crossing 331 within a cardiaccycle, a local maximum 334 or a local minimum 335 after an absoluteminimum 333 within a cardiac cycle, an absolute minimum 333 within acardiac cycle, or a local maximum 336 above a zero crossing 337 after anabsolute minimum 333 within a cardiac cycle. The timing circuit 230 mayalso be configured to calculate a time interval between a point on theheart sound signal 340 representing an S2 heart sound 342, and any oneof the following points on another transformed signal of a cardiacimpedance signal—a point indicative of a maximum systolic blood flowwithin a cardiac cycle, an aortic valve opening within a cardiac cycle,a pulmonary valve closure within a cardiac cycle, an aortic valveclosure within a cardiac cycle, or mitral valve opening within a cardiaccycle. Also, as another example, the timing circuit 230 may beconfigured to calculate the time interval between a point on the heartsound signal 340 representing an S1 heart sound 341, and any one of thefollowing points on the first derivative signal 330—a first zerocrossing 331 within a cardiac cycle, a local minimum 335 or a localmaximum 334 after an absolute minimum 333 within a cardiac cycle, or alocal maximum 336 above a zero crossing 337 after an absolute minimum333 within a cardiac cycle. The timing circuit 230 may also beconfigured to calculate the time interval between a point on the heartsound signal 340 representing an S1 heart sound 341, and any one of thefollowing points on a transformed cardiac impedance signal—a pointindicative of an aortic valve opening within a cardiac cycle, apulmonary valve closure within a cardiac cycle, or a mitral valveopening within a cardiac cycle. As yet another example, the timingcircuit 230 may be configured to calculate a time interval between apoint on the heart sound signal 340 representing an S3 heart sound 343,and any one of the following points on the first derivative signal330—an absolute minimum 333 within a cardiac cycle, a local maximum 334or a local minimum 335 after an absolute minimum 333 within a cardiaccycle, or a local maximum 336 above a zero crossing 337 after anabsolute minimum 333 within a cardiac cycle. The timing circuit 230 maybe configured to calculate a time interval between a point on the heartsound signal 340 representing an S3 heart sound 343, and any one of thefollowing points on a transformed cardiac impedance signal—a pointrepresenting an aortic valve closure within a cardiac cycle, a pulmonaryvalve closure within a cardiac cycle, or a mitral valve opening within acardiac cycle. These are just examples of some of the intervals that maybe analyzed between a heart sound signal 340 and a first derivative 330or other transformed signal of a cardiac impedance signal 320.

The information and data that may be obtained from the calculation ofthese time intervals may be used for many purposes. For example, thetiming circuit 230 may be configured to calculate one or more of thesetime intervals over multiple cardiac cycles, and further configured tothen use the data from these multiple cardiac cycles to identify anepisode of heart failure decompensation as a function of one or morechanges in the time interval over the multiple cardiac cycles. Forexample, if the left ventricular ejection time (LVET) is decreasing overmultiple cardiac cycles, then this may indicate that the left ventricleis pumping less blood for each systolic contraction, indicating that thepatient's heart condition is worsening. As another example, if thepre-ejection period (PEP, or pre-ejection time) is increasing overmultiple cardiac cycles, then that may indicate that contraction of theheart is taking longer, thereby taking more time to build up pressure inthe heart chambers, which can result in less blood in the left ventricleto be pumped to the body during systole. In this example, PEP may bedefined as the interval from the start of electrical left ventricledepolarization to the onset of aortic ejection in early systole. Thisinterval can be approximated by the time difference between a point onthe QRS complex (such as the R-wave or a pacing spike) and a point onthe transformed impedance cardiogram that corresponds to an onset ofaortic flow, such as 331 in FIG. 3C. Similarly, PEP can also beestimated using the heart sounds waveform by using a point in the S1waveform complex that corresponds to an aortic opening.

A ratio of the LVET and PEP intervals can be used to estimate leftventricle stroke volume and cardiac output. In a patient withprogressively worsening heart failure, as alluded to above, the LVETdecreases and the PEP increases. Therefore, relative increases in apatient's PEP/LVET ratio can be used to alert health care providers ofpotentially diminished cardiac output. Furthermore, a calibratedPEP/LVET ratio can be used as an instantaneous estimate of a patient'scardiac output or stroke volume.

As it relates to one or more examples in this disclosure, heart failuredeocompensation further includes thoracic fluid accumulation andpulmonary edema. One or more examples in this disclosure can heartfailure disease status, progression, and the onset of heart failuredecompensation which may lead to hospitalization. However, an earlyalert to the onset of decompensation by one or more of the examples ofthis disclosure may lead to therapeutic interventions which may preventthe hospitalization or reduce its duration. An example of a therapeuticintervention may involve an implantable drug delivery system such asdrug dispensing circuit 255.

In general, any time interval between any points on one or more of thecardiac signal 310, the cardiac impedance signal 320, the firstderivative signal 330, the heart sound signal 340, and a transformationof the cardiac impedance signal 320 may be analyzed over multiplecardiac cycles to determine if that interval is increasing or decreasingover time. A study may be performed among a population to determine therelationship between any particular time interval and the progression orregression of the patient's heart condition. After such a relationshipis identified, then that relationship may be applied to otherindividuals, such as to identify a progression or regression of anindividual patient's heart condition based on that particular timeinterval.

In certain examples, more complex analyses of heart sound data andcardiac depolarization data may be implemented, such as where theimplantable device 110 includes a cardiac sensing circuit 240, anensemble averaging circuit 245, and a telemetry circuit 235, and furtherwhere an adjunct or external system 160 includes a memory circuit 164and a timing circuit 166. For example, an ensemble average may becalculated for a plurality of cardiac signals and a plurality of heartsound signals. The calculation of an ensemble average, among otherthings, performs signal conditioning by removing noise from the cardiacand heart sound signals, and can further perform compression.

The timing circuit 166 of the external device 160 may be configured tocalculate a time interval between a point on the ensemble averagedcardiac depolarization signal and a point on the ensemble averaged heartsound signal. The timing circuit 166 could further be configured tocalculate a time interval between a first point on the ensemble averagedheart sound signal and a second point on the ensemble averaged heartsound signal. For example, the point on the ensemble averaged cardiacsignal may represent a portion of an R wave, and the point on theensemble averaged heart sound signal may represent a portion of one ofan S1, S2, S3, or S4 heart sound. For example, the first point on theensemble averaged heart sound signal may represent an S1 heart sound andthe second point on the ensemble averaged heart sound signal mayrepresent an S2 heart sound.

The memory 164 in the external device 160 and/or the database 169 mayinclude a patient medication history, a disease history, ahospitalization history, and/or population statistics. The processor 161of the external device may then be configured to use this data inanalyzing an individual's data. The processor 161 may further beconfigured to compute a trend in any time interval relating to thisdata. The external device 160 may further be communicatively coupled toone or more external sensors 168. These external sensors may collectphysiological data from the patient (e.g., blood pressure). The externaldevice may then set one or more patient thresholds as a function of datareceived from the one or more external sensors.

Based on the data and/or trend in the cardiac and heart sound data, theexternal device 160 may transmit a signal to the implantable device 110.This signal can be used to modify the therapy of the device 110. Thesignal can alter the pacing of the electrical delivery circuit 250,alter the level of a pharmaceutical dispensed by the drug dispensingcircuit 255, and/or alter the level of stimulation by the neuralstimulation circuit 260. The electrical delivery circuit 250 may alterpacing pulses delivered to a heart, such as by altering the pacing rate,the pulse width, the pulse amplitude, and other features. The locationof the heart to which the pulse is delivered may also be altered.Similarly, the AV delay or other interelectrode delay of the pulses maybe altered. As these therapies are altered, the device 110 may thencollect additional cardiac and heart sound data, this data may betelemetered to the external device 160, and the external device mayre-calculate the cardiac and heart sound intervals to determine theeffect that the change in therapy had on those intervals.

FIG. 4 illustrates an example of a process 400 that calculates a timeinterval between a point on a cardiac impedance signal and a heart soundsignal, and a point on a first derivative of a cardiac impedance signaland a point on a heart sound signal. In other examples, functions ofthese signals can be used such as multiple derivatives, filteredsignals, and other transformations of a cardiac impedance signal. At405, a cardiac impedance signal is measured. At 410, a first derivativeof that cardiac impedance signal is calculated. At 415, a heart soundsignal is measured. At 417, the time interval between a point on acardiac impedance signal and a point on a heart sound signal iscalculated, and at 420, the time interval between a point on the firstderivative of the cardiac impedance signal and a point on the heartsound signal is calculated.

As further indicated in FIG. 4, the process 400 may use one of severalpoints on the first derivative signal and one of several points on theheart sound signal. For example, at 425, the calculation of the timeinterval between a point on the first derivative of the cardiacimpedance signal and a point on the heart sound signal may include aleft ventricular ejection time. As further indicated at 427, this leftventricular ejection time may be calculated by using a point on theheart sound signal representing an S1 heart sound, and a point on thefirst derivative representing an absolute minimum within a cardiaccycle. Similarly, as indicated at 430, the process 400 may calculate atime interval between a point on the first derivative of the cardiacimpedance signal and a point on the heart sound signal that results inthe pre-ejection time. At 432, the pre-ejection time is calculated, suchas by using a point on the heart sound signal representing an S4 heartsound, and a point on the first derivative representing a first zerocrossing within a cardiac cycle. At 435, the process 400 calculates atime interval, such as by using a point on the heart sound signalrepresenting an S4 heart sound, and a point on the first derivativerepresenting an absolute maximum within a cardiac cycle. At 440, theprocess 400 calculates a time interval, such as by using a point on theheart sound signal representing an S2 heart sound, and a point on thefirst derivative representing one of an absolute maximum within acardiac cycle, a first zero crossing within a cardiac cycle, a localmaximum or a local minimum after an absolute minimum within a cardiaccycle, an absolute minimum within a cardiac cycle, or a local maximumabove a zero crossing after an absolute minimum within a cardiac cycle.At 445, the process 400 calculates a time interval, such as by using apoint on the heart sound signal representing an S1 heart sound, and apoint on the first derivative representing one of a first zero crossingwithin a cardiac cycle, a local minimum or a local maximum after anabsolute minimum within a cardiac cycle, or a local maximum above a zerocrossing after an absolute minimum within a cardiac cycle. This time maybe used to approximate the isovolumic contraction time (IVCT). At 450,the process 400 calculates a time interval, such as by using a point onthe heart sound signal representing an S3 heart sound, and a point onthe first derivative representing one of an absolute minimum within acardiac cycle, a local maximum or a local minimum after an absoluteminimum within a cardiac cycle, or a local maximum above a zero crossingafter an absolute minimum within a cardiac cycle.

At 460, the process 400 calculates a time interval, such as one or moreof the above disclosed time intervals, over multiple cardiac cycles, andidentifies a decompensation or other condition as a function of a changein the time interval over the multiple cardiac cycles.

In another example process includes the steps of measuring a cardiacimpedance signal with an implantable medical device, measuring a cardiacelectrical signal with the implantable medical device (the cardiacelectrical signal including an R-wave), measuring a heart sound signalwith the implantable medical device (the heart sound signal including anS2 heart sound), transforming the cardiac impedance signal into atransformed signal (the transformed signal including a portionindicative of an aortic opening), estimating a pre-ejection time bycalculating an interval between the R-wave on the cardiac electricalsignal and the aortic opening on the transformed cardiac impedancesignal, and estimating a left ventricular ejection time by calculatingan interval between the S2 heart sound on the heart sound signal and theaortic opening on the transformed cardiac impedance signal. The processmay further include calculating a ratio of the pre-ejection time and theleft ventricular ejection time. In this process, the transformation ofthe cardiac impedance signal can include one or more of differentiation,a filtering, a derivation, and an integration.

In the above detailed description of embodiments of the disclosure,various features are grouped together in one or more embodiments forstreamlining the disclosure. This is not to be interpreted as reflectingan intention that the claimed embodiments of the invention require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the detailed description of embodiments, witheach claim standing on its own as a separate embodiment. It isunderstood that the above description is intended to be illustrative,and not restrictive. It is intended to cover all alternatives,modifications and equivalents as may be included within the scope of thedisclosure as defined in the appended claims. Many other embodimentswill be apparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein,”respectively. Moreover, the terms “first,” “second,” and “third,” etc.,are used merely as labels, and are not intended to impose numericalrequirements on their objects.

As used in this disclosure, the term “circuit” is broadly meant to referto hardware, software, and a combination of hardware and software. Thatis, a particular function may be implemented in specialized circuits, insoftware executing on general processor circuits, and/or a combinationof specialized circuits, generalized circuits, and software.

The abstract is provided to comply with 37 C.F.R. 1.72(b) to allow areader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. A processor-readable medium, comprising instructions that, whenperformed by the processor, cause the processor to: obtain informationindicative of an acoustic signal from an implantable acoustic sensor;identify a first heart sound feature in the information indicative ofthe acoustic signal; obtain information indicative of a cardiacimpedance from an implantable cardiac impedance sensor; transform theinformation indicative of the cardiac impedance to obtain transformedcardiac impedance information; identify a first cardiac impedancefeature in the transformed cardiac impedance information; determine afirst interval between the identified first heart sound feature in theinformation indicative of the acoustic signal and the identified firstcardiac impedance feature in the transformed cardiac impedanceinformation; and determine a heart failure decompensation status usinginformation about the determined first interval.
 2. Theprocessor-readable medium of claim 1, wherein the first intervalcorresponds to a left ventricular ejection time (LVET), and wherein theinstructions include instructions that, when performed by the processor,cause the processor to: determine a second interval corresponding to apre-ejection period (PEP); determine a relative indication ofinformation between the PEP and the LVET; and determine the heartfailure decompensation status using the relative indication ofinformation.
 3. The processor-readable medium of claim 2, wherein theinstructions to determine the relative indication of information includeinstructions to determine a ratio of the PEP to the LVET.
 4. Theprocessor-readable medium of claim 3, comprising instructions that, whenperformed by the processor, cause the processor to: determine respectiveinstances of the ratio of the PEP to the LVET corresponding torespective cardiac cycles; identify a trend in the determined respectiveinstances of the ratio of the PEP to the LVET; and determine a heartfailure decompensation status using information about the identifiedtrend.
 5. The processor-readable medium of claim 4, wherein theidentified trend includes identified information indicative of anincreasing ratio of the PEP to the LVET.
 6. The processor-readablemedium of claim 2, comprising instructions that, when performed by theprocessor, cause the processor to: obtain information indicative ofcardiac electrical activity from an implantable cardiac electricalactivity sensing circuit; identify a cardiac electrical activity featurein the information indicative of the cardiac electrical activity; andidentify a second feature heart sound feature in the informationindicative of the acoustic signal; wherein the instructions that, whenperformed by the processor, cause the processor to determine the secondinterval between the identified cardiac electrical activity feature andthe second heart sound feature.
 7. The processor-readable medium ofclaim 1, comprising instructions that, when performed by the processor,cause the processor to: determine respective instances of the firstinterval corresponding to respective cardiac cycles; and identify atrend in the determined respective instances of the first interval;wherein the instructions to determine the heart failure decompensationstatus using information about the determined first interval includeinstructions to determine the heart failure decompensation status usinginformation about the identified trend.
 8. The process-readable mediumof claim 7, wherein the first interval corresponds to a left ventricularejection time (LVET); and wherein the identified trend includesidentified information indicative of a decreasing LVET over multiplecardiac cycles.
 9. The processor-readable medium of claim 1, wherein theinstructions to transform the cardiac impedance information includeinstructions to obtain information indicative of respective slopesbetween respective points in the information indicative of the cardiacimpedance.
 10. The processor-readable medium of claim 1, wherein theinstructions to transform the cardiac impedance information includeinstructions to obtain information indicative of a derivative of theinformation indicative of the cardiac impedance.
 11. An implantablemedical device comprising: an acoustic sensor configured to provideinformation indicative of an acoustic signal obtained using the acousticsensor; a cardiac impedance sensing circuit configured to provideinformation indicative of a cardiac impedance obtained using the cardiacimpedance sensing circuit; a transform circuit coupled to the cardiacimpedance circuit and configured to receive the information indicativeof the cardiac impedance and configured to provide transformed cardiacimpedance information; and a processor circuit communicatively coupledto the to the acoustic sensor and to the transform circuit, theprocessor circuit configured to: receive the information indicative ofthe acoustic signal; identify a first heart sound feature in theinformation indicative of the acoustic signal; receive the transformedcardiac impedance information; identify a first cardiac impedancefeature in the transformed cardiac impedance information; determine afirst interval between the identified first heart sound feature in theinformation indicative of the acoustic signal and the identified firstcardiac impedance feature in the transformed cardiac impedanceinformation, the first interval corresponding to a left ventricularejection time (LVET); determine a second interval corresponding to apre-ejection period (PEP); determine a relative indication ofinformation between the PEP and the LVET; and determine a heart failuredecompensation status using information about the relative indication ofinformation.
 12. A system, comprising: an implantable medical devicecomprising: an acoustic sensor configured to provide informationindicative of an acoustic signal obtained using the acoustic sensor; acardiac impedance sensing circuit configured to provide informationindicative of a cardiac impedance obtained using the cardiac impedancesensing circuit; and a transform circuit coupled to the cardiacimpedance circuit and configured to receive the information indicativeof the cardiac impedance and configured to provide transformed cardiacimpedance information; and a processor circuit communicatively coupledto the to the acoustic sensor and to the transform circuit, theprocessor circuit configured to: receive the information indicative ofthe acoustic signal; identify a first heart sound feature in theinformation indicative of the acoustic signal; receive the transformedcardiac impedance information; identify a first cardiac impedancefeature in the transformed cardiac impedance information; determine afirst interval between the identified first heart sound feature in theinformation indicative of the acoustic signal and the identified firstcardiac impedance feature in the transformed cardiac impedanceinformation; and determine a heart failure decompensation status usinginformation about the determined first interval.
 13. The system of claim12, wherein the first interval corresponds to a left ventricularejection time (LVET), and wherein the processor circuit is configuredto: determine a second interval corresponding to a pre-ejection period(PEP); and determine a relative indication of information between thePEP and the LVET; and determine the heart failure decompensation statususing the relative indication of information.
 14. The system of claim13, wherein the processor circuit is configured to determine therelative indication of information including determining a ratio of thePEP to the LVET.
 15. The system of claim 14, wherein the processorcircuit is configured to: determine respective instances of the ratio ofthe PEP to the LVET corresponding to respective cardiac cycles; identifya trend in the determined respective instances of the ratio of the PEPto the LVET; and determine a heart failure decompensation status usinginformation about the identified trend.
 16. The system of claim 15,wherein the identified trend includes identified information indicativeof an increasing ratio of the PEP to the LVET.
 17. The system of claim13, wherein the processor circuit is configured: obtain informationindicative of cardiac electrical activity from an implantable cardiacelectrical activity sensing circuit; identify a cardiac electricalactivity feature in the information indicative of the cardiac electricalactivity; identify a second feature heart sound feature in theinformation indicative of the acoustic signal; and determine the secondinterval between the identified cardiac electrical activity feature andthe second heart sound feature.
 18. The system of claim 12, wherein theprocessor circuit is configured to: determine respective instances ofthe first interval corresponding to respective cardiac cycles; identifya trend in the determined respective instances of the first intervalcorresponding to respective cardiac cycles; and determine the heartfailure decompensation status using information about the identifiedtrend.
 19. The system of claim 18, wherein the first intervalcorresponds to a left ventricular ejection time (LVET); and wherein theidentified trend includes identified information indicative of adecreasing LVET over multiple cardiac cycles.
 20. The system of claim12, further comprising an adjunct device; and wherein the processorcircuit is included as a portion of the adjunct device.